Biologically active substances, when being lipid-soluble, may be barely added to foods such as drinks in many cases. For example, a hydrophobic licorice component that is extracted from licorice or a residue of water extraction of licorice using an organic solvent or the like has been confirmed to exhibit many useful effects such as an antioxidative effect, an antibacterial effect, an enzyme inhibitory effect, an antitumor effect, an antiallergic effect, and an antiviral effect. Nevertheless, this hydrophobic licorice component is not dissolved in water and cannot be readily added directly to water-based foods. In addition, the hydrophobic licorice component is barely dissolved in general oils. Furthermore, this component in the form of an organic solvent extract is used with difficulties due to its instability such as easy consolidation or coloring.
Thus, for example, Patent Literature 1 employs a method involving mixing a hydrophobic licorice extract with a fat-based solvent containing 10% or more of an oil-soluble polyhydric alcohol fatty acid ester. This hydrophobic licorice component-containing fat composition, however, cannot be solubilized directly in a water-based material or the like.
Patent Literature 2 discloses that a hydrophobic flavonoid of licorice dissolved in medium-chain fatty acid triglyceride is prepared into an oil-in-water emulsion in the presence of an emulsifier. This technique, however, is merely directed to water dispersibility and is not aimed at transparency or acid resistance.
Patent Literature 3 proposes a composition containing an oily extract of licorice and polyglycerin lauric acid ester. Its acid resistance or heat resistance, which is required for addition to drinks, is not sufficient.
Patent Literature 4 discloses a licorice polyphenol-containing oil-in-water emulsion composition containing a polyglycerin fatty acid ester composed of a fatty acid residue having 14 or more carbon atoms. Its production requires a homogenization treatment under high-pressure conditions of 50 MPa or higher.
Patent Literature 5 discloses a fat-solubilized composition comprising a polyglycerin having an average degree of polymerization of 6 to 10 and a monoester of saturated fatty acid having 12 to 14 carbon atoms. Its production requires a homogenization treatment under high-pressure conditions of 135 MPa or higher.
Patent Literature 6 discloses an oil-soluble substance-solubilized composition comprising a polyglycerin having an average degree of polymerization of 5 to 10 and a monoester of myristic acid or oleic acid. Its production requires a homogenization treatment under high-pressure conditions of 100 MPa or higher.
Patent Literature 7 discloses a self-emulsifying preparation comprising polyoxyethylene sorbitan fatty acid ester. This preparation reportedly forms a microemulsion upon contact with an aqueous medium. Use of the polyoxyethylene sorbitan fatty acid ester in foods, however, is strictly limited in Japan or other countries. Thus, this preparation cannot be applied to a wide range of foods.
Patent Literature 8 discloses a stable aqueous composition containing an oil-soluble substance solubilized or dispersed in a water-soluble medium using a special polyglycerin saturated fatty acid ester having a clouding point of 20° C. or higher.